Permeability mechanism of PVC-P geomembranes based on low-field NMR technology

The permeability of plasticized polyvinyl chloride (PVC-P) geomembranes (GMBs) is of significant importance to the safe operation of the impermeable structures and even the project. To avoid the drawbacks of adopting the permeability coefficient to characterize permeability traditionally, this paper presents a mathematical model of porosity and seepage discharge based on the results of the vertical permeability test and porosity obtained from low-field nuclear magnetic resonance (NMR) test, and the applicability of porosity to evaluate the permeability was explored combined with the dynamic distribution of pores and pore radius. The results show that the low-field NMR technology with 1H atoms as the probe can accurately measure the distribution of pores and pore radius in the PVC-P GMB. The proportion of micropores (Mic), mesopores (Mes) and macropores (Mac) and the shrinkage or development of pore radius are primarily responsible for the variation of the porosity. The porosity is closely correlated with the seepage discharge, and the constructed model can accurately predict the seepage discharge. Furthermore, the porosity can provide technical support for the evaluation of the permeability of PVC-P GMBs and the selection of appropriate GMBs for engineering design.